For detecting the presence of excessive or dangerous fuel gases in the atmosphere of a house, mobile home or industrial plant use has been made of a catalytic, resistive gas sensing element, for example, a wire coated with platinum black. Electrical current supplied to the element heats the element to a temperature at which it will oxidize fuel, e.g. propane or butane, leaking into the atmosphere. Oxidizing the fuel further heats the wire causing an increase in its resistance, which increase can be detected in various ways. One way of detecting the resistance change is by connection of the catalytically coated element in a Wheatstone bridge together with a similar compensating resistive wire element which is uncoated and hence unresponsive to fuel gas. Upon sensing an excessive amount of gas the detector can cause an alarm to be sounded and a gas valve to be closed.
One difficulty with such gas detectors arises if the coated sensing element or compensating element burns open, or a battery power supply weakens. A false alarm resulting from such failures may result or the premise may be left unprotected.
It is an object of the present invention to provide a detector which generates a trouble signal in the event of failure while preventing false alarming. A further object is to signal weakening of the power supply without affecting capability of the detector to alarm. A still further object is to energize a gas cut-off valve only once for each incidence of alarm.